The noble gases are, for all intents and purposes,
chemically inert - that is that they do not react. Examination
of their electronic configurations reveals that, except for helium,
they all have the filled s and p orbitals, i.e., ns2np6. This
observation suggests that we can attribute their lack of chemical
reactivity to this filled s and p electronic configuration.

Noble Gas Electronic Configurations

Noble Gas

Electronic congifuration

He

1s2

Ne

[He]2s2 2p6

Ar

[Ne]3s2 3p6

Kr

[Ar]3d10 4s2
4p6

Xe

[Kr]4d10 5s2
5p6

Rn

[Xe]4f14 5d10
6s2 6p67

The lesson we take away from this observation
is that the ns2np6 electronic configuration is very stable. We
can expect that any element or ion that is isoelectronic with
a noble gas will also be stable. This observation is known as
the noble gas or "octet" rule.